What Can I Put on My Garden to Kill the Weeds & Grass Before It Is Time to Till It?

Tillers aren't designed to clear large amounts of existing grass and weeds.

Installing a new garden in your yard means clearing the area and removing the existing vegetation. Pulling all the grass and weeds in the area by hand is difficult and time-consuming, but several options exist to kill them before you till the area. What time of year you till affects which products work best.

Nonselective Chemical Herbicide

Some herbicides work only on specific plants, such as broadleaf or grassy weeds. Although these herbicides can help you in your quest to clear the garden area, they aren't effective against both weeds and grass. For that, you need a nonselective, postemergent herbicide such as one containing glyphosate. Grass and weeds absorb this herbicide through their leaves, transporting it through their vascular systems to the roots. Glyphosate kills most plants quickly, often in just a couple of days. The advantage of glyphosate is that it doesn't dwell in the soil; it breaks down quickly, which means you can till and begin planting your garden as soon as the grass and weeds die. Some vegetables, such as tomatoes (Solanum lycopersicum), are more sensitive to any glyphosate residue, so wait at least a couple of weeks before planting them. Using a ready-to-use spray, apply the herbicide directly to the grass and weeds, making sure that it has at least 30 minutes to dry before the area gets wet from rain or sprinklers.

Tilling Right Away

Some herbicides help kill young grass and weeds and are safe enough to till into the soil where you plan to plant your garden. Products such as trifluralin for broadleaf weeds and sethoxydim for grass and grassy weeds won't harm your vegetable seeds after you till and plant, even though they don't disappear from the soil as quickly as glyphosate. They work best on newly emerging weeds and grass. Follow the manufacturer's instructions when mixing the liquid concentrates, such as adding an ounce of the concentrate to 1 gallon of water before spraying the weeds and grass.

Organic Alternative

Instead of introducing chemicals to your garden, try vinegar as an organic alternative. The acetic acid in vinegar works as a nonselective herbicide, burning the leaves and blades of weeds and grass. It doesn't leave harmful residue in the soil, which makes it safe to add before you till and plant. Pour household vinegar onto the plants; it works best on sunny days when the sun helps increase the burning effect of the acid. Garden supply stores offer higher concentrations of vinegar for a stronger burn; household vinegar is a 5 percent solution, but 10 and 20 percent vinegar solutions also exist. When handling the stronger solutions, wear protective gear such as gloves and safety goggles.

Application Timing

Herbicides tend to work best when the grass and weeds are actively growing. For most weeds, this is in the spring; you can kill the grass and weeds and then till the area right before you're ready to plant. When you apply herbicides in the fall, it might take more than one application to kill plants that are already preparing for winter dormancy. Tilling alone won't necessarily kill the grass and weeds, which can regrow from the roots or seeds that become distributed under the soil during tilling.